Showing papers by "Carlos Cativiela published in 1988"
TL;DR: In this article, the chiral dienophile N-acryloyl-L-phenylalanine methyl ester was made to react with cyclopentadiene.
Abstract: To test whether α-amino acids can be efficient chiral auxiliaries in asymmetric Diels–Alder reactions, the chiral dienophile N-acryloyl-L-phenylalanine methyl ester was made to react with cyclopentadiene. Diastereofacial selectivity is to a great extent dependent on the Lewis acid used to promote the reaction; whereas moderate excesses of the (1R,2R)-cycloadduct were achieved with AlCl3, the reaction did not show diastereofacial selectivity when titanium catalysts were used. Moreover, with Ti(iPrO)4 a transesterification reaction, which leads to the isopropyl ester and competes with the Diels–Alder reaction, was observed. In spite of the structural similarity of this dienophile to the acrylate of (S)-ethyl lactate, it behaved very differently in the titanium-catalyzed reactions.
16 citations
TL;DR: In this article, the hydrogenation of the tetrasubstituted alkene moieties of the prochiral didehydro amino acid derivatives (1a and b), (2a, b, (3b), (+)- and (−)-(6, (+)-(7), and (−)-(9) was successfully achieved under very mild homogeneous conditions (1 atm of H2; 293 K) by using iridium complexes of the type [Ir(cod)(bzn)(L)][ClO4][cod = cycle-oct
Abstract: The hydrogenation of the tetrasubstituted alkene moieties of the prochiral didehydro amino acid derivatives (1a and b), (2a and b), (3b), (+)- and (–)-(6), (+)-(7), and (–)-(9) has been successfully achieved under very mild homogeneous conditions (1 atm of H2; 293 K) by using iridium complexes of the type [Ir(cod)(bzn)(L)][ClO4][cod = cycle-octa-1,5-diene, bzn = benzonitrile, L = tricyclohexylphosphine, (–)-neomethyldiphenylphosphine, or (+)-phenyl-(o-methoxyphenyl)methylphosphine] as catalyst precursors. The presence of chiral groups in the catalysts or in the unsaturated substrates produces little optical induction; the enantiomeric excesses obtained were less than 27% in all cases.
14 citations
TL;DR: In this article, the authors expressed their gratitude to the Diputacion General de Aragon and Paula Charro to the Instituto de Estudios Riojanos for a grant.
Abstract: This research was made possible by the generous financial support of the Comision Asesora de Investigacion Cientifica y Tecnica (project number PB85-0335). Maria P. Bueno would like to express her gratitude to the Diputacion General de Aragon and Paula Charro to the Instituto de Estudios Riojanos for a grant.
14 citations
TL;DR: The authors showed that the methyl group does not essentially affect the phenyl ring-double bond planarity and applied the Klopman-Salem equation to the reaction of E-2-phenyl-4-benzylidene-5(4H)-oxazolone with different amines.
Abstract: Reactions of (Z/E)-2-phenyl-4-(α-arylethylidene)-5(4H)-oxazolones and Z-2-phenyl-4-arylmethylene-5(4H)-oxazolones with nucleophiles occur with retention of the exocyclic double bond geometry, whereas reactions of E-2-phenyl-4-arylmethylene-5(4H)-oxazolones with some nucleophiles occur with total or partial isomerization. Structural calculations, MMPI and AM1, on model compounds reveal that the methyl group does not essentially affect the phenyl ring-double bond planarity. Application of the Klopman-Salem equation to the reaction of E-2-phenyl-4-benzylidene-5(4H)-oxazolone with different amines, calculated by MNDO, points to a reversible nucleophilic attack at the exocyclic carbon of this 5(4H)-oxazolone as a possible explanation of this behaviour
6 citations